In his consulting room in a suburb of Montgomery, Alabama, gastrologist Randy Brinson is a worried man. A staunch Republican and devout Baptist, Dr Brinson can claim substantial credit for getting George Bush re-elected in 2004. It was his Redeem the Vote initiative that may have persuaded up to 25 million people to turn out for President Bush. Yet his wife is receiving threats from anonymous conservative activists warning her husband to stay away from politics.

"They've been calling my house, threatening my wife," said Dr Brinson. "The first time was on a day when I was going up to Washington to speak to Republicans in Congress. Only they knew I'd be away from home. The Republicans were advised not to turn up to listen to me, so only three did so."

The reason he has fallen foul of men whose candidate he helped re-elect is that he has dared to question the partisan tactics of the religious right. "Conservatives speak in tones that they have got power and they can do what they want. Only 23% of the population embraces those positions but if someone questions their mandate or wants to articulate a different case, for the moderate right, they are totally ridiculed."

In his office in Washington DC, Rich Cizik, vice-president of the National Association of Evangelicals, the largest such umbrella group in the US, is also feeling battered. His mistake has been to become interested in the environment, and he has been told that is not on the religious right's agenda.

Mr Cizik, an ordained minister of the Evangelical Presbyterian church and otherwise impeccably conservative on social issues such as abortion, stem-cell research and homosexuality, believes concern for the environment arises from Biblical injunctions about the stewardship of the Earth. The movement's political leadership, however, sees the issue as a distraction from its main tactical priorities: getting more conservatives on the supreme court, banning gay marriages and overturning Roe v Wade, the 1973 abortion ruling.

"It is supposed to be counterproductive even to consider this. I guess they do not want to part company with the president. This is nothing more than political assassination. I may lose my job. Twenty-five church leaders asked me not to take a political position on this issue but I am a fighter," he said.

Another Washington lobbyist on the religious right told the Guardian: "Rich is just being stupid on this issue. There may be a debate to be had but ... people can only sustain so many moral movements in their lifetime. Is God really going to let the Earth burn up?"

Such partisan tactics are perhaps to be expected in a divisive political climate, with both sides excoriating each other in moralistic terms in a way that has not been seen in Europe for many years - and which is increasingly incomprehensible to many Europeans.

To Judge Roy Moore, who was unseated as chief justice of the Alabama supreme court in 2003 for refusing to remove a five-tonne granite monument on which were carved the Ten Commandments from the court's foyer, that just shows how far Europe has slid.

Judge Moore, campaigning in the state's primaries to supplant the incumbent Republican governor, during a visit to address a women's club in the town of Enterprise, told the Guardian America was falling into Godlessness, too: "That's it, we're going the same way England is now, without God. Is it true that Islam is taking over there?" he asked.

This is a common idea in rightwing circles and, if some of the arguments sound overheated - a recent radio discussion in Virginia on stem-cell research took it as read that only Christians were capable of moral decisions - the religious right has reason to fear that its reach is declining.

"I would rather put my .38 pistol in a child's room than put a computer or a television set there. The devil's crowd is working how to get to your children," declared Brother Richard Emmett in his Mothering Sunday sermon, broadcast to audiences in eastern Tennessee. There is a sense that some of the evangelists - using the medium that Brother Emmett reviles so much - may have overreached themselves. Jerry Falwell, founder of the Moral Majority, and Pat Robertson have embarrassed their followers by antics such as blaming the terrorist attacks of September 11 2001 on "the pagans and the abortionists and the feminists and the gays and the lesbians who are actively trying to make an alternative lifestyle ... to secularise America".

More influential than either is James Dobson of Focus on the Family, who broadcasts daily to the nation from the organisation's Colorado Springs headquarters. Focus on the Family refused to speak to the Guardian, saying "we have no interest in assisting your research", but Washington journalist Dan Gilgoff says Mr Dobson has moved towards an increasingly partisan stance. Mr Dobson endorsed Mr Bush in 2004 but also unsuccessfully rallied the faithful in defence of Judge Moore's monument and threw his weight behind Harriet Miers' disastrous candidacy for the supreme court last year. Nevertheless, Mr Gilgoff says, "people are scared of crossing him". Mr Dobson is one of those warning Mr Cizik off environmental issues.

But these are ageing leaders, with no comparable successors in sight. And, after years of campaigning against abortion and gays, they have not succeeded in getting their way on either issue. There have been victories, but the president's pledge of a constitutional amendment defining marriage as a heterosexual partnership has not happened.

That does not mean religion is going away as a lobbying force. Dr Brinson has started advising the Democrats on how to get more religion into their politics in the hope of winning the constituency back in the presidential race of 2008. And, if religious broadcasting grates, as one woman in Tennessee told me: "I just turn up the rock music on the radio."

Backstory

Religion has always played its part in politics in the United States but, following the 2004 election, the religious right could claim to have made the difference between President George Bush's victory and defeat. The president increased his vote by 9 million, of which 7 million were Catholics - even though his challenger John Kerry is Catholic.

A report from the Pew Forum, the Washington-based religion and public life research centre, said: "The 2004 exit poll showed that a whopping 78% of white evangelicals voted for President Bush and that they comprised 23% of the overall electorate, making them by far the single most potent voting block in the electorate."

The Pew Forum found: "Whether a person regularly attends church (or synagogue or mosque) was more important in determining his or her vote for president than such demographic characteristics as gender, age, income and region and just as important as race."